This invention relates to molten metal metering and transfer devices and more particularly to such devices for use with cold chamber casting machines.
Two different types of molten metal metering and transfer devices are commonly used today to supply the molten metal used in castings. One type of device is commonly known as a hot chamber and is generally employed with low temperature metals such as zinc, or lead. A second type of device is commonly termed a cold chamber and is more commonly utilized with high temperature materials such as aluminum, magnesium and bronze.
Hot chambers generally take the form of a gooseneck structure which is partially or completely emersed in a molten metal bath. The molten metal enters the gooseneck structure through an entry port, and a piston seated in the gooseneck structure is actuated by a hydraulic system forcing the molten metal up through the gooseneck and out an exit sprue into the mold to be filled. This type of device requires a piston and hydraulic assembly which are strong and can overcome the pressures exerted by the molten metal, in order to push the molten metal into the casting. The distance moved by the hydraulically controlled piston is determined not by the amount of material to be displaced but by the amount of material necessary to fill the casting and by the pressure developed when the casting has been filled.
With cold chamber devices, a chamber is located outside of a molten metal bath and is connected at one end to a die casting machine. A piston and hydraulic operator are connected to the cylinder at the other end. Between the two ends, somewhat closer to the piston, is an input or fill port. Molten metal from a bath is usually brought to this fill port by way of a trough extending from a molten metal bath to the cylinder. The cylinder is commonly termed a shot sleeve.
In a hand operation, the operator dips a ladle into the molten metal, then raises the ladle to the top of the bath resting the ladle bowl on the top of the bath adjacent the trough. The ladle is then tipped allowing the molten metal in the ladle to flow into the trough and to the shot sleeve. The operator attempts to visually coordinate the amount of metal necessary in the shot sleeve and the amount of metal dispersed from the ladle. In such a hand operation, dispersing a uniform amount is difficult. Furthermore, because of the manner in which the ladle is pivoted over onto its side to allow exit of the molten metal, it is difficult to control the amount of metal which is dispersed and the speed at which it flows. Consequently, the dispersing of a uniform amount on each use is difficult and potentially dangerous should an excessive amount be released which overflows the trough.
Most attempts at automating the metering and transfer procedure used in a cold chamber utilize equipment and devices which attempted to copy identically the motions of the machine operator in a hand operation. In these systems, a ladle is dipped into the molten metal bath then slowly raised and pivoted over into the trough until the molten metal flows into the trough. Some systems, instead of pouring out of a lip on the ladle, pour through a hollow in the handle so that the ladle only had to be dipped, then pivoted back and up in order to disperse the molten metal. In any case, these systems have the same deficiencies as with the hand ladling. Specifically, the amount of material picked up into a ladle and then dispersed cannot be controlled with any degree of accuracy. Because the dispersal of the molten material is a function of gravity, there is great danger that once the coefficient of friction for the material has been exceeded due to pivoting of the ladle, a large mass of the molten metal will begin to flow very rapidly and could not be controlled so that a danger of spillage and injury is present.
A second type of molten metal metering and transfer device is utilized wherein the molten metal in the bath is maintained in a hermatically sealed container. Pressure is applied to the bath in the container so that the molten metal is forced upward in the container. The molten metal forced upward is expelled through a small aperture near the top of the housing which connects with the trough coupled to the shot sleeve.
In this type of apparatus, a great many parts are required and the operation is quite complex and dangerous. Application of excessive pressure without checks can cause an explosion which would send molten metal flying through the air. It is very difficult to control the precise amount of material expelled upon application of a specific amount of pressure because of the lack of homogeninity in molten metal which is partially caused by the passage of air under pressure through the molten metal. In any case, as noted, these versions are extremely complex and expensive in order to provide all of the controls necessary for proper and safe operation.